Drumlins

Drumlins are depositional landforms made of glacial till, and they are among the most telling features a glacier leaves behind. Their shape and orientation are not random — they record the direction in which the ice once moved, which makes them valuable for reconstructing past glaciation.

A drumlin is a smooth, oval-shaped, ridge-like feature. It is composed mainly of glacial till, though some masses of gravel and sand may also be present within it. The long axis of a drumlin lies parallel to the direction of ice movement, so the entire feature is elongated in the same line along which the glacier travelled.

In terms of size, a drumlin may measure up to 1 km in length and about 30 m in height. These dimensions make them prominent but not towering features on a glaciated landscape.

The two ends of a drumlin are distinctly different. The end that faces the glacier is called the stoss end, and it is blunter and steeper than the opposite end. The other end, called the tail, is gentler and more tapered. This asymmetry is the key to reading the direction of ice flow.

Drumlins form when rock debris is dumped beneath heavily loaded ice. The debris passes through fissures in the glacier and gets deposited under the ice itself. Once deposited, the stoss end is blunted by the pushing action of the moving ice, which sculpts it into its characteristic steep face while the tail trails off in the direction of movement. …